I have an 08 sierra z71 with 64000 miles. I hear a sort of high pitch whinning noise from the rear.  It's hardly noticable to anyone else, but I notice the difference after completing a 550 mile trip towing a loaded trailor.  The total weight of the trailor loaded is probably around 5000 lbs.  My engine never ran hot.  I'm sure I didn't overload the truck.  I checked trans. fluid it was at proper level.  Any one with experience on this?
				
			
	